The present invention relates to a rod type linear motor comprising a coil member having a polyphase coil and a rod-like member having a cylindrical body made of a non-magnetic material and a plurality of plate-like segment magnets which are accommodated in the cylindrical body such that they are stacked in the axial direction of the cylindrical body, wherein a polyphase alternative current is applied to the polyphase coil of the coil member to produce a shifting magnetic field, thereby moving the rod-like member or the coil member. The present invention also relates to a linear guiding apparatus employing the linear motor as a driving means.
FIGS. 1(A), 1(B) are illustrations showing a schematic structure of a conventional rod type linear motor of this kind. As illustrated, a linear motor 100 comprises a rod-like stationary member 110 and a movable member 120. The rod-like stationary member 110 comprises a cylindrical body 111 made of non-magnetic material (for example, stainless steel) and disc-like segment magnets 112 which are accommodated in the cylindrical body 111 and stacked in the axial direction of the cylindrical body 111 such that the same poles of the adjacent segment magnets 112 confront each other (the N-poles of segment magnets confront the N-poles of the respective adjacent segment magnets and the S-poles of segment magnets confront the S-poles of the respective adjacent segment magnets). The movable member 120 comprises a polyphase coil 121 (in the illustrated example, a three-phase coil consisting of phases U, V, and W) surrounding the rod-like stationary member 110. FIG. 1(A) is a longitudinal sectional view of the linear motor and FIG. 1(B) is a cross sectional view of the linear motor.
In the rod type linear motor 100 having the aforementioned structure, as a three-phase alternating current is applied to the polyphase coil 121 (three-phase coil consisting of phases U, V, W) of the movable member 120, a shifting magnetic field is produced. Because of magnetic interaction between the shifting magnetic field and magnetic fluxes generated from a large number of segment magnets 112 of the rod-like stationary member 110, the movable member 120 moves in directions of arrows A and B. The movable member 120 may comprise a core (iron core) and may not comprise the core, that is, may be coreless.
In the rod type linear motor 100 having the aforementioned structure, since the rod-like stationary member 110 includes the disc-like segment magnets 112 accommodated in the cylindrical body 111 made of a non-magnetic material and stacked in the axial direction of the cylindrical body 111, the rod-like stationary member 110 may be deflected due to its own weight when the linear motor 100 is arranged horizontally so that there is a problem that the increase in span (length) of the linear motor 100 is not allowed. In case of using such a rod type linear motor 100 as a driving means for a linear guiding apparatus in which a movable block moves along a rail, the rod-like stationary member 110 is often arranged parallel to the rail and substantially horizontally so that the rod-like stationary member 110 should be deflected if its length is increased. There is a problem that, if the deflection is grown, the suitable gap between the polyphase coil 121 and the rod-like stationary member 110 can not be kept according to the travel of the movable member 120. Accordingly, there is a problem that it is impossible to realize the linear guiding apparatus having a large traveling range.
In case of using the rod type linear motor as the driving means for the linear guiding apparatus as mentioned above, to achieve large thrust, it is necessary to increase the diameter of the disc-like segment magnets 112 to generate increased fluxes. However, in the linear guiding apparatus of this kind, there is a limitation on increase of the space between the rails so that the rod-like stationary member of the linear motor must be disposed in the limited width. Therefore, there is a problem that large thrust can not be achieved due to the limitation on increase in diameter of the section of the cylindrical rod-like stationary member.